1. Field of the Invention
The present invention relates to a method of selecting a base station, and a mobile station, a base station, and a recording medium recording program wherein the most appropriate base station is selected from a plurality of base stations, when a mobile station in a wireless network establishes a relay connection with a communication network.
2. Description of the Related Art
Generally, in a wireless network such as a cellular system, a wireless LAN system employing base stations, and the like, there are a plurality of base stations relay-connected to an external communication network and a mobile station connected to these base stations via radio channels. The most appropriate base station from the plurality of base stations is selected when the mobile station communicates with the communication network.
FIG. 11 is showing the overall architecture of a wireless network adopting a prior art method of selecting a base station. The wireless network 100 shown in FIG. 11 comprises a relay server 102 connected to an external communication network 101, four base stations 103 relay-connected to the relay server 102, and a mobile station 104 connected to these base stations 103 via radio channels.
In this network, the routing path is configured such that, the relay server 102 connects to a first base station 103A, the first base station 103A to a second base station 103B, the second base station 103B to a third base station 103C, and the third base station 103C to a fourth base station 103D.
For example, in communicating with the relay server 102, the mobile station 104 receives base station selection signals from the first base station 103A, the second base station 103B, the third base station 103C, and the fourth base station 103D to measure reception status of the received base station selection signals.
By measuring reception status such as received power of respective base station selection signals, the mobile station 104 selects a base station from base stations 103. The selected base station has an optimal reception status based on the measured results. The mobile station 104 connects to the relay server 102 for communication by establishing a wireless connection with the selected base station 103.
Thus, according to a prior art method of selecting a base station, the mobile station 104 can measure reception status such as received power of respective base station selection signals to select the base station 103 with an optimal reception status based on the measured results.
There is another prior art method of selecting a base station according to which respective base stations 103 receive signals about reception status sent from the mobile station 104, and send the received status to a control station or the like. The control station can select a base station 103 with an optimal reception status based on the received status.
To summarize, according to such prior art methods of selecting a base station, communication qualities between the mobile station 104 and base stations 103 may be collected so as to select a base station with the best communication quality, for example, one that has the highest received signal power as the most appropriate station for the wireless connection of the mobile station 104.
According to the above-described prior art methods of selecting a base station, a base station 103 that provides the highest communication quality with the mobile station 104 is selected as the most appropriate base station for the wireless connection of the mobile station 104. For example, when the mobile station 104 establishes a relay connection with the relay server 102, if communication with the fourth base station 103D provides the best quality, even though communication with the first base station 103A may also provide high quality, the fourth base station 103D will be selected as the most appropriate base station. Thus, the mobile station 104 will establish a wireless connection with the fourth base station 103D. However, this will lead to increased traffic between base stations 103 compared to the case where the mobile station 104 establishes a wireless connection with the first base station 103A, for example, since the traffic from the mobile station 104 destined for the relay server 102 travels through the fourth base station 103D, the third base station 103C, the second base station 103B, and the first base station 103A to reach the relay server 102. Consequently, the transmission delay between the mobile station 104 and the relay server 102 will also be increased.
According to the above described prior art methods of selecting a base station, while the case where paths between the base stations 103 are established via wired channels has been described, a multi-hop network in which paths between the base stations 103 are established via radio channels could be employed. In such cases, communication qualities will be significantly affected by not only communication qualities between the mobile station 104 and the base station 103D, but also communication qualities of the wireless links along the relay paths between the mobile station 104 and the relay server 102.
For example, the third base station 103C might be selected as the most appropriate base station, since communication between the mobile station 104 and the third base station 103C providing the best quality. Nevertheless, there are cases where many wireless links are involved along the paths from the third base station 103C to the relay server 102 so that communication between the mobile station 104 and the relay server 102 does not necessarily provide the best quality even though the third base station 103C is selected as the most appropriate station.